用所给动词的适当形式填空
1. He _____(learn) English for 8 years.
2.I'm so tired, I  ____ ( drive) for eight hours without a rest.
3. You _____ ( do)  the report since six o'clock. Let's have a rest.
4. We ____ ( write)  English for two hours.
5. Your mother ____(look) for you all the morning.
6. Helen  _____    ( leave) her keys in the office,so she had to wait
    until her husband _____( come) home.
7. I ____( hope) to meet Mr. Thompson this morning,but I found nobody left in the room.
8. We plan to reach the North Pole in mid-July,and by then we _____  ( walk)  for six weeks.
9. By the time you arrive in New York,you will ____  ( away) for  two weeks.
10. -Did you find the missing couple in the mountain yesterday?
      -No,but we  ____( try) to get in touch with them ever since.